Testing H2S Scavengers Polymerization Factors

ABSTRACT

Scavenging chemicals used in mitigation treatments of hydrogen sulfide in hydrocarbon streams often continue to react and form polymers that foul the processing system. Disclosed herein are methods for determining if a scavenging chemical mitigator, or its reaction or degradation product, will polymerized during or after mitigation treatments. This information allows for the optimization of mitigation treatments that pre-emptively control or prevent polymer formation. Such pre-emption measures reduce the cost and time related to remedial actions to treat polymer-fouled equipment.

PRIOR RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 17/338,104, filedJun. 3, 2021 (Allowed, published US20210389255), which claims priorityto U.S. Ser. No. 63/039,781, filed Jun. 16, 2020 (expired). Each isexpressly incorporated by reference herein in its entirety for allpurposes.

FEDERALLY SPONSORED RESEARCH STATEMENT

Not applicable.

REFERENCE TO MICROFICHE APPENDIX

Not applicable.

FIELD OF THE DISCLOSURE

The disclosure relates generally to hydrogen sulfide mitigationtreatment. Specifically, methods of screening chemical mitigators todetermine if the chemicals or their reaction products will polymerize inhydrocarbon-containing streams after mitigation, and methods ofscreening components or compositions for modifying the polymerizationare disclosed. Avoiding polymerization averts costly cleaning efforts toreduce or eliminate the problematic polymerization products, and ensuresthat hydrogen sulfide mitigation treatment remains cost effective.

BACKGROUND OF THE DISCLOSURE

Hydrocarbon fluids and gases often contain a variety of sulfurcompounds. When sulfur is present in concentrations of 1 percent or moreby weight, the hydrocarbon is characterized as “sour,” whereasconcentrations of 0.5 percent or less are “sweet” hydrocarbons. It iswell known that sulfur compounds contained in hydrocarbon streams arecorrosive and damaging to metal equipment, particularly copper andcopper alloys. Sulfur has shown a particularly corrosive effect onequipment such as brass valves, gauges and in-tank fuel pump coppercommutators.

One such destructive sulfur compound is hydrogen sulfide (H₂S). Hydrogensulfide is a toxic, corrosive gas produced through the breaking down oforganic sulfur compounds by sulfate-reducing bacteria (SRBs). Oncehydrogen sulfide is detected in a hydrocarbon stream, it is necessary tomitigate hydrogen sulfide's impacts and bring the hydrocarbon stream tothe desired specifications. Unfortunately, hydrogen sulfide is not foundin isolation, but together with methane, hydrogen and higherhydrocarbons, as well as traces of nitrogen-, oxygen-, calcium-, andmetal-containing species, all of which complicate the selection of themost suitable hydrogen sulfide mitigation technique.

There are multiple biological, chemical, and mechanical/operational(physical) mitigation techniques from which to choose amongst, accordingto the hydrocarbon stream characteristics, hydrogen sulfideconcentration, economic considerations, and other variables. Biologicalmitigation techniques focus on removing hydrogen sulfide from water inwastewater treatment plants, but have not been used for hydrocarbonstreams.

Mechanical mitigation techniques include releasing hydrogen sulfide intothe atmosphere at wellheads, pumps, piping, separation devices, oilstorage tanks, and water storage vessels. Flaring is also used to burngases that would otherwise present a safety problem. It is common toflare natural gas that contains hydrogen sulfide to convert the hydrogensulfide gas into less toxic compounds.

The oil and gas industry has previously utilized nitrogen strippingsystems to remove the hydrogen sulfide. Nitrogen is an inert gas thatprevents the flammable gases from igniting and thus eliminates the riskof explosion. Once the hydrogen sulfide has been separated from the gas,it can be converted to a waste product that can safely be disposed of orused in the manufacturing of sulfur. However, it is difficult and costlyto transport the liquid nitrogen that these stripping systems need.Thus, physically stripping hydrogen sulfide from hydrocarbon streams maynot be cost effective.

Chemical mitigation techniques utilize additives to scavenge and absorbhydrogen sulfide. Caustic soda wash absorbs and removes small quantitiesof hydrogen sulfide from natural gas and refinery gases. Additionally,iron oxide, either fixed in an Iron Sponge or free flowing, is used toscavenge and remove hydrogen sulfide and mercaptans from natural gas.

Another class of scavengers are formaldehyde releasing chemicals calledtriazines. Triazines react with hydrogen sulfide to provide asubstantially non-toxic compound or a compound which can be removed fromthe hydrocarbon. Currently, the most frequently used triazine hydrogensulfide scavengers are hexahydrotriazines, including monoethanolamine(MEA) triazine and monomethylamine (MMA) triazine. These triazines areeffective scavengers that are available at reasonable cost and arereadily deployable in scrubbers or in a production train that can bephysically located adjacent to hydrocarbon sources such as gas wells.

Though triazines are the most popular chemical mitigators, they do havesome disadvantages. FIG. 1A displays the chemical reaction between MEAtriazine and hydrogen sulfur. The triazine reacts with hydrogen sulfide,resulting in the release of an MEA ‘arm’. Under extreme conditions thatare not present at all hydrocarbon-containing reservoirs, the reactionis able to proceed until trithiane forms.

When the MEA triazine is spent to a high level, or when the reactionwith hydrogen sulfide has proceeded very far along its pathway, thedithiazine reaction product exceeds its solubility in the aqueous mediumand comes out of solution as a highly dense layer. Once formed, thisdense liquid layer can undergo one of two outcomes. It may simplycrystallize to the monomeric species in large cubic crystals, as hasbeen isolated and observed in field fluids. Under certain conditions,however, dithiazine may undergo a secondary, polymerization reactionthat involves opening of the dithiazine ring to form amorphousdithiazine which is a highly insoluble polysulfide, per FIG. 1B.

Amorphous dithiazine deposits present a significant problem to the gasprocessing industry. The deposits can form blockages in gas processingequipment, storage tanks, truck tanks, and water disposal wells. Cleanupprocedures are time consuming and difficult. Often, the equipment has tobe taken off-line so the deposits can be manually chipped away. Thismakes cleaning up amorphous dithiazine deposits an expensive venture.

U.S. Pat. No. 8,920,568 discloses a method of treating the amorphousdithiazine buildup with a solution of hydrogen peroxide. The hydrogenperoxide reacts with the amorphous dithiazine at temperatures between65-70° C. and breaks apart the buildup for easy removal. Peroxidesalone, however, are very aggressive to oil and gas assets, and cannot beused without the necessary additives designed to mitigate these negativeeffects. WO2018001604 teaches the use of an organic peroxide as anamorphous dithiazine dissolver, together with a selected corrosioninhibitor (CI) to avoid corrosion of oil field equipment. However,removal of the dithiazine deposits is still costly and time consumingeven with these methods.

What is needed in the art is a simple and safe method for testing forconditions that lead to polymerization of chemical mitigators or theirreaction products such that steps can be taken to prevent the formationof polymer deposits and/or such steps optimized. If amorphousdithiazine, or other polymers with solubility problems, do not form,there is no need to take remedial action. Ideally, this method isreliable with a high throughput to quickly screen various conditions,components, or compositions in the ongoing mitigation of hydrogensulfide downstream, midstream or upstream.

SUMMARY OF THE DISCLOSURE

Described herein are methods for determining if chemicals, such astriazines, bis-oxazolidines, and other formaldehyde-based scavengers,used for mitigation of hydrogen sulfide in fluids will continue to reactafter mitigation treatments to form polymers that deposit and foul theequipment.

During mitigation treatments, triazines and bis-oxazolidines scavengersreact with the hydrogen sulfide to remove it from the fluids. Thesesulfide scavengers are often added in excess to ensure complete removalof the hydrogen sulfide. However, the reaction products or degradationof the spent scavengers, such as formaldehyde, amines, or dithiazine(DTA), are capable of forming polymers that can foul equipment under theright conditions and often in the presence of hydrogen sulfide.

The presently described methods combine known amounts of the reactantsfor the mitigation process (e.g. one or more chemical sulfidescavenger(s) plus a sulfide source), reaction products, and/ordegradation product(s) with optional components or additives such assolvents, buffers, acids/bases, salts, alcohols, amines (primary,secondary, tertiary and quaternary), water soluble polymers, anddispersants to form test mixtures.

These test mixtures are then processed under various conditions andanalyzed using e.g., spectroscopy to determine if polymers form and, ifso, quantify the amount of polymer formation to determine if it islikely to deposit on the equipment. This results in a reliable, highthroughput screening method for determining which treatment conditions,components, or compositions will inhibit or induce polymerization.

Once the degree of polymer formation is known for specific treatmentconditions, pre-emptive measures to reduce polymer fouling can beselected and performed before or during the hydrogen sulfide mitigationtreatments. These pre-emptive measures are typically time and costeffective compared to any post-polymerization remedial efforts to cleanfouled equipment.

An advantage of the present methods is that they are high throughputanalyses, allowing the screening of a large number of conditions at thesame time. Once the samples are processed, they are analyzed usingcommon analytical instrumentation. In some embodiments, spectroscopictechniques are used for analysis. It takes mere minutes to obtain anabsorbance measurement using a spectroscopic technique such asultraviolet-visible (“UV-Vis”) or Raman spectroscopy. Thus, pH,treatment temperatures, reaction times, concentration and identity ofpolymerization inhibiting additives, concentration and identity ofsolvents, and the like can be systematically varied and tested rapidlyto determine its effect on the polymerization. This allows for the quickdetermination of adjustments that can be made to the mitigationtreatment process to reduce or eliminate polymer fouling.

In other embodiments, turbidity meters are used for analysis as they toomeasure a loss in a light beam intensity as it passes through a sample.Chromatographic techniques and mass spectrometry can also be usedseparately or in combination to analyze the processed samples to measurepolymer presence and/or concentration.

In some embodiments, UV-Vis is utilized for the high throughputanalyses. Any wavelength, or range of wavelengths, can be used as longas there is no molecular absorption interfering with the signal. In someembodiments, absorption measurements are taken at 900 nm as most organicmolecules do not absorb this wavelength. Thus, any reduction in thelight transmission will be due to the particles in the solutionscattering light. The absorption measurements for each sample can becompared to an appropriate blank sample to measure the degree of polymerformation, including reduction or inhibition of polymer formation.

A further advantage is the testing of various reaction mixtures andconditions in a low-risk small scale environment. This allows forobservation of dangerous mixtures and other hazards, without foulingexpensive equipment, as well as quick testing of measures to reduce oreliminate polymerization and other reactions resulting in the fouling ofproduction equipment. Once appropriate measures are determined toprevent or reduce polymerization, the measures can be scaled up tohigher-risk production environments.

Any pre-emptive measure can be taken before or during the mitigationtreatment of hydrocarbon-containing fluids once the extent ofpolymerization has been determined in the small scale tests. By way ofexample, a pre-emptive measure that can be taken before hydrogen sulfidemitigation treatments is combining a selection of mitigation chemicalsand polymerization inhibiting additives to offset or reduce polymerformation while reducing or removing hydrogen sulfide. Alternatively, assome of these polymerization reactions are temperature dependent, thefluid to be treated can be cooled before being scrubbed, or duringmitigation treatment, to prevent or reduce polymerization. This alsoallows for very high scavenger spend rates with little to no polymerfouling. Other pre-emptive methods of reducing polymerization includeadjusting the pH or over-injecting the scavenger. In over-injecting thescavenger, about 35-40% of the scavenger will be used to scavenge thehydrogen sulfide while the remaining 60-65% prevents polymerization.

The methods are applicable to all hydrocarbon streams that are fluids(liquid and gas), including crude and refined hydrocarbons. However, itshould be expected that certain pre-emptive measures will work betterfor some hydrocarbon streams, temperatures, and/or pH conditions.

The present methods include any of the following embodiments in anycombination(s) of one or more thereof:

A method of identifying conditions that influence (e.g., reduce,eliminate, induce or otherwise modify) polymer formation in sulfidescavenger treatments comprising the steps of preparing an array ofsamples wherein each sample has a sulfide scavenger and a sulfide in abuffer and, optionally, at least one additional component, andprocessing the samples to induce polymer formation.

At least one parameter in one or more samples in the array is varied,including pH, processing temperature, processing time, concentration andidentity of sulfide scavenger, concentration and identity of sulfide,and concentration and identity of the additional component. In someinstances, two or more parameters may be modified at once, but itgenerally preferred to change a single parameter at a time. Each samplemay also be present in duplicate, triplicate, or more.

After processing, the samples are analyzed to measure degree of polymerformation. One or more parameter(s) that reduce polymer formation is/areselected and can either be re-tested to further optimize the treatmentor can be implemented as is into the sulfide mitigation treatment. Forexample, if we find that one reagent seems to reduce fouling at low pHand cooler temperatures, that same reagent can be tested at a range oflow pH and temperature values to determine what the optimal conditionsof usage are.

A method of optimizing a sulfide mitigation treatment comprising thesteps of preparing an array of samples wherein each sample hasdithiazine in a buffer and, optionally, at least one additionalcomponent, and processing the samples to induce polymer formation. Atleast one parameter in each of one or more samples in the array isvaried, including e.g., pH, processing temperature, processing time,concentration of dithiazine, and concentration and identity of theadditional component(s). The samples are then analyzed to measure thedegree of polymer formation. The cycle is repeated as needed foroptimization, and one or more parameter(s) that minimize or eliminatepolymer formation is then selected and implemented into the nowoptimized sulfide mitigation treatment.

A method for analyzing an array of samples, comprising the steps ofpreparing an array of samples wherein each sample has aformaldehyde-releasing sulfide scavenger and a sulfide in a buffer and,optionally, at least one additional component. Next, processing thesamples to induce polymer formation by heating the samples for a periodof time and then cooling the samples to a temperature of 30° C. or lessfor a period of time. At least one parameter in one or more samples inthe array is varied, including e.g., pH, heating temperature, heatingtime, concentration and identity of formaldehyde-releasing sulfidescavenger, concentration and identity of sulfide, or concentration andidentity of the additional component. The reaction product for eachsample in the array of samples is then analyzed to detect formation of apolymer. Additional steps such as determining which parameter(s)minimize or eliminate polymer formation and implementing the parameterinto a sulfide mitigation treatment can be taken to optimize thescavenging/mitigation treatment.

A method of quantifying polymer formation comprising the steps ofpreparing an array of reaction samples wherein each reaction sample hasdithiazine and at least one additional component in a buffer andpreparing at least one blank sample with dithiazine in the buffer. Thesamples are then processed to form a reaction product within each sampleand analyzed to measure the degree of polymer formation in the reactionproduct of each reaction sample using UV-Vis compared to the blanksample. For the reaction samples, parameters that may minimize polymerformation in the reaction product can be varied, including e.g., the pH,concentration of dithiazine, concentration and amount of each additionalcomponent, heating temperature, heating time, heating rate, coolingtemperature, and/or cooling time.

Any method herein described, wherein the additional component is asolvent, an acid, a base, a dispersant, a salt, an alcohol, amines(primary, secondary, tertiary and quaternary), water soluble polymers orcombinations thereof.

Any method herein described, wherein the processing step includesheating the samples at a known heating rate to a known temperature for aknown amount of time; and, cooling the samples to a temperature at orbelow 30° C. for a known amount of time. The processing step can furthercomprise varying a processing parameter in one or more samples in thearray of samples, wherein the processing parameter is selected fromheating temperature, heating time, heating rate, cooling temperature,and cooling time.

Any method herein described, wherein the analyzing step uses anUltraviolent-Visible (UV-Vis) spectrometer to measure polymer formation.

-   -   Any method herein described, wherein the sulfide source is        selected from a group consisting of lithium sulfide, sodium        sulfide, potassium sulfide or magnesium sulfide.

Any method herein described, wherein the analyzing step includes thesteps of comparing the UV-Vis absorbance of each sample with theabsorbance of a blank sample that underwent the same processing steps.

Any method herein described, wherein the at least one additionalcomponent is a solvent or a solvent selected from a group consisting ofmonoethanolamine, methanol, triethylene glycol, or monoethylene glycol.

-   -   Any method herein described, wherein the at least one additional        component is an acid or a base to change the pH of one or more        samples.

Any method herein described, wherein the at least one additionalcomponent is a dispersant.

Any method herein described, wherein the at least one additionalcomponent is a water soluble polymer; or a water soluble polymerselected from a group comprising polyvinyl sulfonate,polyvinylpyrrolidone, cellulose, polyethylene oxide, polysaccharide,derivatives thereof, and combinations thereof.

Any method herein described, wherein the at least one additionalcomponent is a salt or an inorganic or organic salt having a counter ionfrom Groups 1 and 2 on the periodic table or a neutral salt, an alkalisalt or an acid salt.

Any method herein described, wherein the at least one additionalcomponent is an amine or a primary, secondary, tertiary or quaternaryamine, and can be selected from a group comprising alkyl amines,alkyl-hydroxy amines, amino acids, amino saccharides, diamines,triamines, alkyl benzyl amines, or combinations thereof. Alternatively,the amine is selected from a group comprising methylamine, propylamine,monoethanolamine, isopropanolamine, tris(2-aminoethyl)amine,glucosamine, ethylene diamine, diethanolamine, diisopropanolamine,methyldiethanolamine, triethanolamine, diethylenetriamine, pyrrolidone,or derivatives thereof.

Any method herein described, wherein the at least one additionalcomponent is an alcohol selected from a group comprising methanol,ethanol, isopropanol, hydroxybenzenes (mono-, di-, and tri), lowercarbon glycols, and combinations thereof.

Any method herein described, wherein the known heating temperature isbetween about 20° C. to about 120° C. and/or the known heating time isat between a few minutes to a few days but preferably is faster, e.g.,5-120 minutes or 30-60 minutes, or preferably about 35 and about 45minutes.

As used herein, the term “triazine” refers to a class ofnitrogen-containing heterocycles made by the reaction of lowalkanolamines and/or methylamines with formaldehyde. These triazineshave the general structures of:

wherein R, R′, and R″ can be the same or different alcohols having aC1-C10 backbone. Exemplary triazines used for the mitigation of hydrogensulfide include, but are not limited to, monomethylamine (MMA) triazineand monoethanolamine (MEA) triazine.

As used herein, the terms “chemical hydrogen sulfide mitigator”,“scavenging chemical”, and “sulfide scavenger” are used interchangeablyto refer to scavengers or absorbents used to reduce or remove hydrogensulfide from fluids.

As used herein, “pre-emptive measures” refers to plans or courses ofactions that are decided upon before a hydrogen sulfide mitigationtreatment commences, although the timing of the implementation of themeasures can occur at any time before or during mitigation treatments.

As used herein, the terms “polymerization inhibitor” and “polymerizationinhibiting additive” are used generally to refer to a chemical orcomposition that can slow, reduce, and/or prevent polymerization.

As used herein, the phrase “chemical mitigation package” refers to thecombination of chemical hydrogen sulfide mitigator(s) and other optionaladditives or components that are used to scavenge hydrogen sulfide whilereducing polymer fouling.

As used herein, the terms “array” or “array of samples” refers to anordered series of two or more samples, wherein at least one variable orparameter in the samples, or processing of the samples, is changed. Asimplified schematic of an array of samples is shown in FIG. 7 .Depending on the number of samples, multiple variables can be modifiedand tested in the array. Further, duplicates and triplicates of a givensample, with the same set of variables and parameters, may be present inthe array. Although each sample in the array typically only has onevariable or parameter changed at a time, as shown in FIG. 7 , it ispossible to have two or more variables changed to evaluate the effect ofthe combination of the variables/parameters.

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims or the specification means one or more thanone, unless the context dictates otherwise.

The term “about” means the stated value plus or minus the margin oferror of measurement or plus or minus 10% if no method of measurement isindicated.

The use of the term “or” in the claims is used to mean “and/or” unlessexplicitly indicated to refer to alternatives only or if thealternatives are mutually exclusive.

The terms “comprise”, “have”, “include” and “contain” (and theirvariants) are open-ended linking verbs and allow the addition of otherelements when used in a claim. The phrase “consisting of” is closed, andexcludes all additional elements. The phrase “consisting essentially of”excludes additional material elements, but allows the inclusions ofnon-material elements that do not substantially change the nature of theinvention. Any of these transition phrases can be interchanged withanother in the claims, but in the interests of brevity, potential claimsare not repeated using different transition phrases.

The following abbreviations are used herein:

ABBREVIATION TERM DTA Dithiazine HPLC High-performance liquidchromatography IC Ion chromatography IPPA Isopropanolamine LC-MS Liquidchromatography-mass spectrometry MALDI-MS Matrix assisted laserdesorption ionization-mass spectrometry MEA Monoethanolamine MEGMonoethylene glycol MeOH Methanol MMA Monomethylamine Py-GC/MS Pyrolysisgas chromatography/mass spectrometry SRB Sulfate-reducing bacteria TEGTriethylene glycol UPLC Ultra-performance liquid chromatography UV-VisUltraviolet-visible spectroscopy

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A. Reaction mechanism between MEA triazine and hydrogen sulfide.

FIG. 1B. Polymerization mechanism for amorphous dithiazine.

FIG. 2 . Exemplary sample vials of dithiazine with no solvent and noheating (Vial A), no solvent and after heating (Vial B); and, increasingamounts of solvent after heating (Vials C-G). The heated samples wereheated at 105° C. for 45 minutes.

FIG. 3 . Effects of increasing amounts of different solvents on theformation of amorphous dithiazine.

FIG. 4 . Effects of increasing amounts of dithiazine on the formation ofamorphous dithiazine.

FIG. 5 . Effects of pH on the formation of amorphous dithiazine.

FIG. 6 . Effects of reaction temperature on the formation of amorphousdithiazine.

FIG. 7 . A simplified schematic of an array of samples wherein only oneparameter is changed per sample.

DESCRIPTION OF EMBODIMENTS OF THE DISCLOSURE

The present disclosure provides a novel method of screening hydrogensulfide scavenging chemical mitigators before mitigation treatments todetermine if these chemical mitigators, or their reaction or degradationproducts, will polymerize after the mitigation treatment begins and foulthe processing equipment. Once the amount of polymer formation, if any,is known, pre-emptive measures to reduce fouling can be performed beforeor during hydrogen sulfide mitigation treatments, instead of expensiveremedial efforts to physically clean fouled equipment afterpolymerization has already presented a problem.

In more detail, the present methods are directed to the detection andquantification of polymerization, if any, formed during or afterhydrogen sulfide mitigation treatment with chemical scavengers. Thescavenging reactions result in reaction products that can react undercertain conditions to form polymers capable of fouling the processingequipment. Formaldehyde-releasing chemical scavengers can also releaseformaldehyde and form one or more degradation products in the presenceof hydrogen sulfide. Like the reaction products, these degradationproducts can also result in the formation of polymers that foul theprocessing equipment. Regardless of the source of the polymers, thefouling results in costly and time-consuming remedial measures to removepolymeric deposits.

The present methods are directed to predicting polymerization activityfor scavenging chemical mitigators such as triazines and oxazolinering-containing compounds under a variety of operating conditions. Thepresent methods screen chemical mitigator packages comprising at leastone scavenging chemical mitigator and a sulfide source, or a scavengingchemical's reaction or degradation product, to determine if polymerswill form after mitigation treatments under particular conditions. Insome embodiments, the elimination, modification, reduction, orinducement of polymerization is tested by combining the chemicalmitigator package with one or more additional components or additives,and/or by modifying one or more operating parameters (pH, temperature,concentrations, and the like). Once the tests are run (either once or inrepeated cycles of testing), the conditions that produce the leastpolymerization can then be selected and implemented as needed in oil andgas production and processing equipment.

Exemplary sulfide scavenging chemicals tested by the present methodsinclude triazines and oxazoline ring-containing compounds such as MMA,MEA, and isopropanolamine (IPPA). Each of these compounds has a reactionproduct, and possibly a degradation product, that can be analyzed usingthe present methods to see if these products contribute topolymerization. For example, dithiazine (DTA) is a reaction product forMEA triazine that can polymerize. DTA can be combined with one or moreadditives, under a variety of conditions (temperature, pH, DTAconcentration), to evaluate the ability to reduce or prevent amorphousdithiazine formation.

Currently, the industry standard for evaluating mitigation chemicals isa test using a sparging apparatus. The sparging apparatus is filled witha specific amount of the chemical mitigator and purged with hydrogensulfide gas to mimic various “spend” levels of the chemical mitigator.Polymerization is then determined by gravimetric means or visibleobservations, neither of which is very sensitive. Further, each samplecan take between 1 to 2 days, or longer, before polymerization occurs.This procedure significantly slows the treatment process.

The presently described methods improve upon the industry standard bycreating a quicker, more sensitive method utilizing analyticalinstrumentation for the detection of polymerization for a variety ofreaction conditions. This results in a high throughput method that canprocess 25 to 45 or more samples a day.

In one embodiment, at least one scavenging chemical mitigator plusadditional optional components are combined with hydrogen sulfide (or asulfide salt) in a buffered solution. The mixtures are processed underone or more sets of reaction conditions, and the resulting products areanalyzed to determine if a polymer formed and measure the amount ofpolymer. This results in a high throughput method for quicklydetermining how a scavenging chemical mitigator or a combination ofscavenging chemical mitigators and other components will polymerizeunder a variety of operational conditions such as reaction temperatures,reaction times, pH, and/or concentrations of the scavenging chemicalmitigator(s). In some embodiments, solvents, acid/bases, dispersants,alcohols, salts, amines (primary, secondary, tertiary and quaternary),water soluble polymers, or other polymerization inhibitors are added tothe sample solution to evaluate their ability to reduce or inhibitpolymerization under various conditions.

In another embodiment, the sample solution is a reaction or degradationproduct of the scavenging chemical mitigator in a buffered solution withan optional additive such as a solvent or other polymerizationinhibitor. As before, the mixtures are processed under one or morereaction conditions, and the resulting products are analyzed todetermine if polymers formed and the amount of polymer. This alternatemethod allows for the direct analysis of a specific reaction ordegradation product, without interference from other products or excesshydrogen sulfides. However, a sulfide source can be added to evaluateits effect on the polymerization of reaction or degradation products.

These embodiments allow for the addition of optional components that maybe included in the hydrocarbon fluid, field solvent, or the chemicalmitigation package. The optional components can be a solvent, apolymerization inhibitor or the like that is used to evaluate one ormore potential pre-emptive measures. Alternatively, the optionalcomponent can be acids/bases for changing the pH of the test samples.

In yet another alternative, the optional component can be inorganic ororganic salts, amines (primary, secondary, tertiary and quaternary),water soluble polymers, dispersants, and/or alcohols. Examples ofoptional components include, but are not limited to, solvents such asmonoethanolamine, methanol, triethylene glycol, monoethylene glycol;water soluble polymers such as polyvinyl sulfonate,polyvinylpyrrolidone, cellulose, polyethylene oxide, or polysaccharide;salts such as inorganic or organic salt having a counter ion from Groups1 and 2 on the periodic table or neutral, alkali, or acid salts;primary, secondary, tertiary or quaternary amines such as methylamine,propylamine, monoethanolamine, isopropanolamine,tris(2-aminoethyl)amine, glucosamine, ethylene diamine, diethanolamine,diisopropanolamine, methyldiethanolamine, triethanolamine,diethylenetriamine, pyrrolidone, or other alkyl amines, alkyl-hydroxyamines, amino acids, amino saccharides, diamines, triamines, alkylbenzyl amines; alcohols such as methanol, ethanol, isopropanol,hydroxybenzenes (mono-, di-, and tri), or lower carbon glycols; and,derivatives and combinations thereof.

Once the test sample is prepared it can be processed under a variety ofconditions. Typically, the test samples are heated at known heatingrates to known reaction temperatures for known amounts of time beforebeing cooled to a known temperature for a known amount of time. Thepresent methods allow for each of these conditions to be varied toevaluate the effects they may have on polymerization inducement,reduction or inhibition.

In some embodiments, the test samples are heated at a reactiontemperature between about 20-120° C. In some embodiments, the testsamples are heated to between about 20-85° C., or between about 80-120°C. or between about 40-105° C. Alternatively, the test samples areheated to about 23° C., 44° C., 48° C., 53° C., 57° C., 66° C., 85° C.,103° C. or 105° C.

The heating time is dependent on the scavenging process and can rangefrom between about 5 minutes to multiple days, though faster times arepreferred. In some embodiments, the heating time is selected based onmeasuring a blank sample heating time in the heater. Alternatively, theheating time is between about 30 minutes to about 60 minutes, morepreferably between 35 and 50 minutes, and most preferably about 45minutes.

After a sample is heated, it is cooled to a temperature that is lessthan about 30° C. to freeze the polymerization process and allow forconsistent analysis. In some embodiments, the heated samples are placedin a water bath having a temperature of about 22° C. If needed, coolertemperatures could also be used, e.g., 4° C. The cooling time depends onthe heating temperature and type of cooling mechanism. If using a waterbath having a temperature of about 22° C., for example, the cooling timecan vary between 5 and 30 minutes, preferably between about 10 and 20minutes, and most preferably about 15 minutes.

Any analytical technique for polymer analysis can be used to evaluatethe presence and amount of polymer formation, if any, in the processedtest samples. Additionally, techniques that are not specific to polymeranalysis, but that can determine the presence of suspended particlessuch as polymers can also be used. Exemplary analytical techniquesinclude, but are not limited to, turbidity meters, UV-Vis spectroscopy,Raman spectroscopy, high-performance liquid chromatography (HPLC),ultra-performance liquid chromatography (UPLC), liquidchromatography-mass spectrometry (LC-MS), ion chromatography (IC),matrix assisted laser desorption ionization-mass spectrometry(MALDI-MS), pyrolysis gas chromatography/mass spectrometry (Py-GC/MS),and the like.

In some embodiments, spectroscopy is used to evaluate the presence of apolymer, and if any, quantify its amount when compared to an appropriateblank sample. Preferably, UV-Vis is used as it can quickly scan a rangeof wavelengths or a single wavelength, allowing for quicker sampleprocessing. In some embodiments, the UV-Vis collects measurements at 900nm as most organic molecules do not absorb this wavelength. Thus, anyreduction in the light transmission will be due to the particles in thesolution scattering light.

Once the presence and amount of polymer for each sample is known,conditions that produced the least polymerization can be used inpre-emptive measures employed before or during chemical mitigationtreatments of a hydrocarbon stream. In some embodiments, the pre-emptivemeasures involve the use of one or more solvents or dispersants whoseperformance was evaluated using the methods disclosed herein. In otherembodiments, the pre-emptive measures involve adjusting operatingconditions such as reaction temperatures, reaction times, or pH in areaction vessel. Combinations thereof are also possible.

A benefit of the high throughput nature of the presently describedmethods is that different reaction conditions, components, compositions,or pre-emptive measures can be tested simultaneously and directlycompared to optimize the chemical mitigation treatments. For example, acombination of scavenging chemical mitigators and other components inthe chemical mitigation package can be tested at different pH, heatingtemperatures, heating times, and/or solvent compositions in the sameday. This not only allows for the optimization of a chemical mitigationpackage for reduced polymerization but also identifies mitigationtreatment conditions (pH, temperature, concentration, solvent content,and the like) that can increase, reduce, modify, or inhibitpolymerization for a given scavenging chemical mitigator. Likewise,different reaction products or degradation products can be quicklyevaluated in the presence of polymerization inhibitors or other optionaladditives.

In some embodiments, the pre-emptive measures are the preparation ofoptimized combinations, or packages, of different kinds of scavengingchemical mitigators, polymerization inhibiting additives, and/orsolvents to reduce or eliminate polymer formation. Alternatively, thescavenging chemical mitigator can be combined with an additive toprevent the scavenging chemical mitigator or its reaction products fromreacting after the hydrogen sulfide has been reduced or eliminated.

In yet another alternative, the scavenging chemical mitigator can becombined with an additive that can slow, reduce, and/or preventpolymerization occurring in the fluid being treated. In anotheralternative, the fluid being treated can be cooled before mitigationtreatments when using a scavenging chemical mitigator having a reactionproduct that polymerizes at high temperatures. Each of these pre-emptivemeasures can be quickly evaluated under a variety of mitigationconditions using the above screening methods.

Any sulfide source can be used in the present methods. While hydrogensulfide is the target analyte in a hydrocarbon stream for mitigationtreatments, hydrogen sulfide is highly toxic and flammable, making itdifficult to work with. Thus, other sulfide sources can be used in thepresent methods. Preferably, sulfide salts are used, such as lithiumsulfide, sodium sulfide, potassium sulfide, magnesium sulfide.

The sulfide salt and scavenging chemical mitigator can be dissolved ordiluted in a buffering solution. The buffering solution may be aninorganic buffer that has a buffering pH between about 6 and about 8,and is soluble in the fluids to be treated. In some embodiments, thebuffering solution is phosphate buffer, e.g., a 1M phosphate buffer.Alternatively, the buffering solutions can comprise a borate-based salt,or mixtures of phosphate and borate buffering salts in concentrationsranging from milliMolar to Molar.

In some embodiment of the present methods, the test samples also includeoptional components such as acids/bases or solvents. A variety of bothpolar and non-polar organic solvents that are normally used in the oiland gas industry can be used in the reaction mixtures in the presentmethods. Alternatively, the optional component is a field solvent. Somefield solvents, such as monoethanolamine, methanol, triethylene glycol,and monoethylene glycol, can also act as polymerization inhibitingadditive. In yet another alternative, the optional component can beinorganic or organic salts that are acidic, alkali, or neutral. In otherembodiment of the present methods, the test samples also includeoptional components that are amines (primary, secondary, tertiary andquaternary), water soluble polymers, dispersants, and/or alcohols. Aswith the polar and non-polar organic solvents, a variety thesecomponents are normally used in the oil and gas industry, and can beused in the reaction mixtures in the present methods.

The disclosed screening methods allow for a quicker and morecost-effective chemical mitigation treatments. The screening methodsdetermine the presence and amount of a polymer for a wide variety ofoperating conditions, scavenging chemical mitigators and their reactionor degradation products, combination of optional components such aspolymerization inhibiting additives, or solvents to solubilize resultingpolymers. This allows an operator to selectively determine the bestchemical mitigation package and/or operating conditions for a reservoirto not only remove the hydrogen sulfide, but also reduce or eliminatefouling of the equipment by avoiding polymerization. This increasesproduction and reduces cost associated with equipment down time andmaintenance.

The following experiments are included to demonstrate embodiments of theappended claims using the above described autometathesis system. Theseexamples are intended to be illustrative only, and not to unduly limitthe scope of the appended claims. Those of skill in the art shouldappreciate that many changes can be made in the specific embodimentswhich are disclosed and still obtain a like or similar result withoutdeparting from the spirit and scope of the disclosure herein. In no wayshould the following examples be read to limit, or to define, the scopeof the appended claims.

The presently disclosed methods were applied to samples comprising pureDTA to evaluate the effects of temperature, pH, DTA concentration andfield solvent effects on amorphous DTA polymerization. Previous proof ofconcept experiments were performed using MEA triazine neutralized withhydrogen sulfide or sodium sulfide to produce DTA. However, theresulting DTA solution contained MEA from the scavenging reaction, whichinfluenced polymerization independent of other additives. Thus, sampleswere prepared using pure DTA, which allows independent factorassessments of temperature, pH, DTA concentration and solvent effects onDTA polymerization.

A 20,000 mg stock solution of DTA (Toronto Research Institute) wasprepared by adding the DTA to a 1M phosphate buffer at pH 7. DTApolymerization releases MEA, a base, which can overcome the phosphatebuffer's buffering capacity if enough MEA is released. As such, allsamples, except those which specifically change DTA concentration, useda standardized concentration of 2000 mg/L of DTA (“standard DTA amount”)in buffer to limit this issue. For the samples used to study the effectsof field solvents, various amounts of the solvents were also added tothe 2000 mg/L DTA solutions.

An aliquot of each sample was heated using a heating block for a knownheating time before being cooled. The heating time and heatingtemperatures were selected based on field conditions. Unless otherwisenoted, the samples were heated to 105° C. for 45 minutes for theexamples described herein. The heating time included the time requiredto heat the samples to the selected temperature and exposure time atthat temperature. Sample containers were cooled to less than 30° C.immediately to “freeze” the polymerization at the given condition.

Samples being used to assess the effects of temperature on DTApolymerization were heated at their respective target temperatures. Asbefore, the heating time was 45 minutes, and, after heating, the samplecontainers were cooled for analysis.

The content of each sample container was quantitatively transferred toanother container with water and diluted. The absorbance measurements ofthe diluted samples were taken using UV-Vis spectroscopy. Each sample'sabsorbance was compared to the most polymerized sample in each series.The blank sample is the most polymerized sample in the examples;however, it is possible to add additives that may increase the extent ofpolymerization, resulting in blank not being the most polymerizedsample. An operator would be able to choose an appropriate blank samplefor comparing the absorbance.

SOLVENT EFFECTS

Four common field solvents—monoethanolamine (MEA), methanol (MeOH),triethylene glycol (TEG), and monoethylene glycol (MEG) —were evaluatedto determine their ability to inhibit the formation of polymerized DTAin heated samples. A series of samples were prepared with varyingamounts of the field solvents being added to the standard DTA amount.The samples were adjusted to ensure the same initial pH conditions andminimal buffer capacity changes, before being processed and analyzed forabsorbance from the polymerization of DTA.

FIG. 2 displays a series of samples with varying amounts of the MEAfield solvent. Vial A is a sample of DTA without MEA before heating, andVial B is DTA without MEA after being heated at 105° C. for 45 minutesand cooled. The sample in Vial B is cloudy and has the highest amount ofturbidity due to the extensive polymerization of the DTA. Vials C-G haveincreasing amounts of MEA, and were also heated and cooled using thesample process as Vial B. These vials show a decrease in the cloudinessor turbidity of the samples, and thus a reduction of the polymerizationof DTA. Hence, we can conclude that MEA inhibits polymerization underthese conditions.

Similar trends in reduction of DTA polymerization were seen with theother three field solvents. As expected, increasing amounts of eachfield solvent reduced the polymerization of DTA. However, under the pHand heating conditions of this example, some inhibiting solvents reducedthe polymerization to a much greater extent than others at lower solventconcentrations. For example, MEA reduced the polymerization to a muchgreater extent at a concentration of about 25 mL/L solution compared toTEG, MEG, and MeOH. Thus, additional samples with a higher concentrationof MEA were prepared and tested.

As shown in FIG. 3 , the reduction in polymerization (decreasedturbidity) occurred rapidly at lower concentrations of before slowingand leveling off with concentrations above about 40 mL MEA/L of thesolution. It was found that the MEA began to have a diminishing effectas MEA concentrations rose past 20 mL/L. As such, other field solventsthat had greater reductions in polymerization at lesser concentrationsmay be preferred depending on the fluid to be treated and operatingconditions.

Other observations include the difference in polymerization reductionusing MEG v. TEG. Though both solvents were glycol based, smalleramounts of TEG were able to decrease the polymerization, and thusturbidity, to a much greater extent than the same volume of MEG. A 5%MEG resulted in only a 20% reduction, compared to the 38% reductionobserved with 5% TEG.

FIG. 3 provides a visual interpretation of the DTA polymerization'sdependence of various field solvents and their concentrations. From thisfigure, it is clear that the relative solvent effectiveness isMEA>>>TEG>MEG>MeOH. The polymerization inhibition mechanism of eachfield solvent is not specifically known. Without being tied to aspecific mechanism, the following mechanisms have been proposed but havenot been confirmed. It is believed that the DTA exist in equilibriumbetween closed ring and open ring structures with polymerizationoccurring in the open ring configuration. MeOH, MEG and TEG may preventDTA molecules from properly orienting so polymerization can occurbetween ring open structures (steric hindrance).

MEA seems have two methods of inhibition: steric hindrance andsubstitution. MEA steric hindrance may work as described above for theother solvents. MEA substitution hypothetically occurs as follows. Asolution phase MEA bonds to the open ring structure at the freeformaldehyde carbon of the DTA, yielding a transient molecule with twoMEAs (one from the solution, the other originally present in DTA). Asthe molecule moves back toward the closed structure, one of the MEA isreleased yielding closed structure DTA and a free MEA (one originallyfrom the solution or one originally present in DTA).

Regardless of the mechanism, each of the evaluated field solvents hassome polymerization inhibition ability towards DTA. It is expected thatthe extent of inhibition of other reaction products, or degradationproducts, will vary for these solvents.

DTA concentration greatly impacts the extent of its polymerization. FIG.4 displays the increase in turbidity as the concentration of DTAincreases. Turbidity rises linearly with concentration until thebuffering capacity is exceeded and then curves over. This figure showsqualitative behavior. However, the higher DTA concentration clearlyincreases polymerization.

As mentioned above, the DTA polymerization reaction releases a base(MEA) that can overcome the buffering capacity if enough MEA isreleased. FIG. 5 shows the drastic change in turbidity with pH change.As can be seen, increasing the pH reduced the polymerization of DTAunder these sample conditions.

For pre-emptive measurements, the pH in a reactor vessel can be raisedto reduce the polymerization and ultimate equipment fouling. In someprocesses, a combination of bases to increase the pH and solvents toreduce polymerization can be used to prevent equipment fouling.

Reaction temperatures were found to greatly impact the polymerization ofDTA. FIG. 6 displays the increase in turbidity as the temperature of thesamples increase. The polymerization slows significantly below 50° C. Inview of these results, process systems can pre-cool scavenging areas asa pre-emptive measure to reduce polymerization. With this adjustment,polymer formation could be reduced even at 90+% MEA triazine spendrates. It is expected that cooling a fluid stream before mitigationtreatments may be combined with other modifications, such as theaddition of field solvents or pH adjustments.

The presently described high-throughput analysis using US-Vis absorbanceallowed for the testing of multiple polymerization conditions in thesame time frame. Understanding what variables can be modified, and howto modify, to reduce or inhibit polymerization allow for the developmentof pre-emptive measures before or during hydrogen sulfide mitigation.While some methods can be cost ineffective (increase pH, decreasetemperatures), adjustments to multiple measures can be combined toreduce or inhibit fouling on the equipment in a cost effective manner.

The following references are incorporated by reference in their entiretyfor all purposes.

-   WO2018001604-   U.S. Pat. No. 8,920,568

1. A method of predicting polymer formation in sulfide scavengertreatments, said method comprising: a) preparing an array of samples,wherein each sample comprises a sulfide scavenger and a sulfide in abuffer and optionally one or more test component(s) selected from asolvent, a buffer, an acid, a base, a salt, an alcohol, an amine, awater soluble polymer, a dispersant, and a polymerization inhibitingadditive; b) varying a parameter in one or more samples in said array ofsamples, said parameter selected from pH, concentration and identity ofsulfide scavenger, concentration and identity of sulfide, heatingtemperature, heating time, heating rate, cooling temperature, coolingtime, concentration of said test component(s) and identity of said testcomponent(s); c) processing said array of samples to induce polymerformation; d) analyzing said processed array of samples to measurepolymer formation; e) selecting one or more parameter(s) and optionallysaid one or more test component(s) that minimize polymer formation; andf) utilizing said selected one or more parameter(s) and optionally saidone or more test component(s) in a sulfide scavenger treatment toprevent polymerization of said sulfide scavenger.
 2. The method of claim1, wherein the processing step c) comprises: a) heating the samples to atemperature between about 40° C.-120° C. for between 5 minutes to up to2 days; and, b) cooling the samples to a temperature at or below 30° C.for between 5 minutes to 30 minutes, wherein, said processing stepfurther comprises varying a processing parameter in one or more samplesin said array of samples, said processing parameter selected fromheating temperature, heating time, heating rate, cooling temperature,and cooling time.
 3. The method of claim 1, wherein said sulfidescavenger is a triazine.
 4. The method of claim 1, wherein said sulfidescavenger is a monoethanolamine (MEA) triazine or monomethylamine (MMA)triazine.
 5. The method of claim 1, wherein said optional additionalcomponent is a solvent selected from a group consisting ofmonoethanolamine, methanol, triethylene glycol, or monoethylene glycol.6. The method of claim 1, wherein said analyzing step comprisesquantitatively measuring the degree of polymer formation.
 7. The methodof claim 1, wherein said analyzing step comprises quantitativelymeasuring the degree of polymer formation by ultraviolet-visible(“UV-Vis”) spectroscopy or Raman spectroscopy.
 8. The method of claim 2,wherein said samples are heated to about 80° C. to about 120° C.
 9. Themethod of claim 8, wherein said analyzing step comprises quantitativelymeasuring the degree of polymer formation by ultraviolet-visible(“UV-Vis”) spectroscopy or Raman spectroscopy.
 10. A method ofpredicting polymer formation in sulfide scavenger treatments, saidmethod comprising: a) preparing an array of samples, wherein each samplecomprises a triazine sulfide scavenger and a sulfide in a buffer andoptionally one or more test component(s) selected from a solvent, abuffer, an acid, a base, a salt, an alcohol, an amine, a water solublepolymer, a dispersant, a polymerization inhibiting additive and apolymerization mitigation chemical; b) varying a parameter in one ormore samples in said array of samples, said parameter selected from pH,concentration and identity of sulfide scavenger, concentration andidentity of sulfide, heating temperature, heating time, heating rate,cooling temperature, cooling time and concentration and identity of saidadditional component(s); c) processing said array of samples to inducepolymer formation; d) analyzing said processed array of samples tomeasure polymer formation; e) selecting one or more parameter(s) andoptionally said one or more test component(s) that minimizes polymerformation; and f) utilizing said selected one or more parameter(s) andoptionally said one or more test component(s) in a sulfide scavengertreatment to prevent polymerization of said sulfide scavenger.
 11. Themethod of claim 10, wherein the processing step c) comprises: a) heatingthe samples to a temperature between about 40° C.-120° C. for between 5minutes to up to 2 days; and, b) cooling the samples to a temperature ator below 30° C. for between 5 minutes to minutes, wherein, saidprocessing step further comprises varying a processing parameter in oneor more samples in said array of samples, said processing parameterselected from heating temperature, heating time, heating rate, coolingtemperature, and cooling time.
 12. The method of claim 10, wherein saidtriazine sulfide scavenger is monoethanolamine (MEA) triazine ormonomethylamine (MMA) triazine.
 13. The method of claim 11, wherein saidanalyzing step uses an Ultraviolent-Visible (UV-Vis) spectrometer tomeasure polymer formation.
 14. The method of claim 10, wherein saidanalyzing step comprises quantitatively measuring the degree of polymerformation.
 15. The method of claim 10, wherein said analyzing stepcomprises quantitatively measuring the degree of polymer formation byultraviolet-visible (“UV-Vis”) spectroscopy or Raman spectroscopy. 16.The method of claim 11, wherein said samples are heated to about 80° C.to about 120° C.
 17. The method of claim 16, wherein said analyzing stepcomprises quantitatively measuring the degree of polymer formation byultraviolet-visible (“UV-Vis”) spectroscopy Raman spectroscopy.